Suspension system, in particular for a working machine

ABSTRACT

The invention relates to a suspension system, in particular for a working machine, such as a tractor or similar, with a suspension cylinder ( 10 ) subject to various load pressures (m), the piston-( 12 ) and rod-side ( 14 ) of which may each be connected to a suspension reservoir ( 16, 18 ), by means of a stop device ( 20 ), which locks the suspension and with an equalization device ( 28 ) which comprises a switching valve ( 48 ) within the supply device, for controlling the piston side ( 12 ) of the suspension cylinder ( 10 ) and with a pressure supply (P) for supplying the system pressure necessary for the suspension system. It is possible to carry out a pressure equalization of the system to the relevant load pressure before renewed operation by means of the equalization device, as said equalization device ( 28 ) comprises a further switching valve ( 50 ) within the supply device ( 30 ) for control of the rod-side ( 14 ) of the suspension cylinder ( 10 ) and a load monitoring device (LS) is connected to parts of the stop device ( 20 ) and the associated suspension reservoir ( 16 ) for the piston side ( 12 ) of the suspension cylinder ( 10 ) in a branch ( 38 ) of a line ( 40 ).

[0001] The invention relates to a suspension system, in particular for a working machine such as a tractor or the like, with a suspension cylinder to which varying load pressures may be applied, a suspension cylinder whose piston and rod side may each be connected as required to a suspension reservoir by way of a locking device which locks the spring suspension system, and with an equalization device having a switching valve for control of the piston side of the suspension cylinder inside the supply device and with a pressure supply for obtaining the system pressure needed in the suspension system.

[0002] In certain spring suspension systems, for example for machines such as tractors or the like, it may be advisable to stop such machines, for example at a speed below an assignable speed of the machine. This is accomplished by locking the hydropneumatic suspension when the vehicle is moving at low speeds or is stationary. Operations such as hoisting and loading and unloading loads or activation of harvesting or other implements may accordingly proceed without disruptive vehicle spring suspension travel.

[0003] Since the load situation is unknown after such operations as the vehicle continues in movement or starts movement, in the known spring suspension systems movement of the vehicle or operating machine is not controlled when the suspension is unlocked; this is in principle an unacceptable situation.

[0004] DE-A-2 023 283 discloses a generic spring suspension system for a machine, such as a construction site vehicle, having two suspension cylinders to which different load pressures may be applied, each of the piston sides of which suspension cylinders may be connected to a suspension reservoir by way of a stop device which locks the suspension and with an equalization device for control of the piston side of the respective suspension cylinder. The generic spring suspension system is used for a suspension device between frame and axletree of a vehicle, consisting of two individual wheel beam supports hinge-connected to the frame by way of a support element connected between the frame and each wheel beam support. Automatic level equalization for the vehicle is achieved with the spring suspension system disclosed; this adjustment may be referred to a central level, the level of a vehicle being understood to mean the position of the vehicle relative to the ground and the distance between a point of the vehicle frame and the ground indicating the level of the vehicle in approximation. Although the disclosed solution achieves an especially soft suspension in addition to the level adjustment, disruptive vehicle spring deflections occur under load, as indicated above.

[0005] DE-C-41 27 917 discloses a spring suspension system comprising a suspension reservoir with piston and rod sides, it being possible to connect the rod side in addition to the rod side also to a suspension reservoir. There is obtained as a type of suspension a supporting force operating in the opposite direction by way of the suspension reservoir for the piston side as well as the rod side of the suspension cylinder; but even with this suspension system the disadvantages of the state of the art cannot be avoided.

[0006] Hence the object of the invention is to develop, starting from this state of the art, a spring suspension system which eliminates the disadvantage described in the foregoing. The desired objective is achieved in full by a spring suspension system having the features specified in patent claim 1 in its entirety.

[0007] Owing to the fact that, as specified in the characterizing part of claim 1, the equalization device has an additional switching valve for control of the rod side of the suspension cylinder within the supply device and owing also to the fact that in a branch line a load monitoring system is connected to a line with components of the locking device as well as to the associated suspension cylinder for the piston side of the suspension cylinder, which load monitoring system controls the pressure supply for the content of the required system pressure, it is possible, by means of the equalization device, to effect pressure equalization of the system on the currently prevailing load pressure before the spring suspension is reactivated. Hence, with the spring suspension system claimed for the invention pressure equalization between the suspension cylinder and the associated suspension reservoir is effected and so uncontrolled movement of the shaft is prevented when the suspension system is engaged, independently of the change in load.

[0008] In a preferred embodiment of the spring suspension system claimed for the invention a sensor device monitors the current operating position of the actuating piston in the suspension cylinder and even slight movement in the area of the suspension cylinder triggers pressure equalization independently of change in load.

[0009] Other advantageous embodiments of the spring suspension system claimed for the invention are specified in the dependent claims.

[0010] The spring suspension system claimed for the invention is discussed in detail on the basis of an embodiment, with reference to the drawings, in which

[0011] FIGS. 1 to 4 illustrate in diagrammatic form a wiring diagram for the spring suspension system claimed for the invention in various states of operation.

[0012] The spring suspension in FIG. 1 is shown in its locked state, that is, the suspension feature proper of the suspension system is disabled.

[0013] The suspension system in question has a suspension cylinder 10 to which varying load pressures m may be applied; the piston side 12 and piston rod side 14 may each be connected to a suspension reservoir 16 or 18 by way of a locking device designated as a whole as 20, the locking device 20 locking the spring suspension in the switched state illustrated. The suspension cylinder 10 is connected by way of its housing to a vehicle body not shown in detail and is linked at the free end of the piston rod 24 connected to the piston 22 to a vehicle wheel 26, a plurality of vehicle wheels together with associated suspension cylinders (not shown) ensuring operability of the machine such as a tractor or the like. The spring suspension system also has an equalization device designated as whole as 28 which engages or disengages the cylinder with the aid of the supply device.

[0014] As FIG. 1 also shows, the two suspension reservoirs 16, 18, which are in the form of conventional hydraulic reservoirs such as membrane reservoirs or the like and the locking device 20 are connected to a supply device designated as a whole as 30, which is to be regarded as part of the equalization device 28 and which ensures connection at option to a pressure supply source P and/or to a tank connection T by way of a switching device designated as a whole as 32. In addition, the two suspension reservoirs 16, 18 are each separable from the supply device 30 by way of a return valve 34, 36 each of which is held in a closed position by a spring under load and move into their open positions in the direction of the relevant suspension reservoir 16 or 18.

[0015] A releasable return valve 43 is mounted in a branch line 38 of the line 40 leading to the closing device 20 of the suspension cylinder 10. Opening control line 41 of releasable return valve 43 is connected to the control line LS of the supply device 30 and a line 45 between the return valve 36 and the 3/2-way switching valve 50. The fluid control connection for this purpose is made at connecting point 47. A response to the load sensing system may be made over the connection for this purpose so that the hydropump P supplying the system may assume system pressure. The releasable return valve 43 itself is connected between lines 38 and 40. In addition to the line 40 on the piston side, an additional line 42 is connected to suspension reservoir 18 and associated return valve 36 on the rod side 14 of the suspension cylinder 10.

[0016] The locking device 20 in question has both for the piston side 12 and for the rod side 14 of the suspension cylinder a 2/2-way switching valve 44, 46 which, while in its inactive basic position shown in FIG. 1, blocks the fluid conducting path from the suspension cylinder 10 toward the suspension reservoir 16, 18 and under spring loading opens the path in the other direction. Hence in the locked position shown in FIG. 1 the suspension cylinder 10, with its piston side 12 and its rod side 14, is separated from the associated suspension reservoirs 16 and 18, and accordingly the suspension system is locked so that spring deflection or rebound of the vehicle (not shown) is not possible and change in load m cannot result in undesirable spring deflection or rebound of the total system.

[0017] The equalization device 28 in question has, both for the piston side 12 and for the rod side 14 of the suspension cylinder 10, within the supply device 30, a 3/2-way switching valve 48 or 50 which in their unactuated initial position are connected to each other by way of a connecting line 52 to the tank connection T and on their admission side are additionally joined together by another connecting line 54 so as to conduct fluid. In addition, the suspension cylinder 10 has a sensor device not shown in detail by means of which it is possible to monitor the position of the piston rod 24 and/or of the piston 22, the sensor device (not shown in detail) forwarding its signals to a data interpretation unit, which in turn activates the switching valves 44, 46, 48, and 50 for an actuation process. Activation for the purpose of effecting pressure equalization prior to activation of the spring suspension will now be explained in what follows.

[0018] First of all reference is made once again to the state of the system as illustrated FIG. 1. In the situation shown the spring suspension is locked and the suspension cylinder 10 is in level position. Deflection or rebound of the piston 22 with piston rod 24 is consequently not possible, since discharge of fluid on the piston side 10 or the rod side 14 is prevented by the switching valves 44, 46 in their closed position. In the locked position as shown, locking by way of switching valves 44, 46 is achieved in that a return valve integrated into them can open in the direction of the suspension cylinder 10, but is kept closed in the opposite direction, that is, in the direction of the suspension reservoir 16, 18. Increased pressure on the suspension reservoir 16, 18 side would thus result in opening of the switching valves 44, 46 even in their locked position in the direction of the suspension cylinder 10. If the load or load pressure m remains unchanged in the switching position shown in FIG. 1, the pressure on the piston side 12 corresponds to the fluid pressure of the suspension reservoir 16 and the fluid pressure on the rod side 14 corresponds to the fluid pressure of the suspension reservoir 18, the pressure on the rod side corresponding to the pressure of the system. In order to prevent, in this situation, uncontrolled movement of the vehicle wheel 26 and accordingly of the movable parts of the suspension cylinder 10 when the suspension is activated, pressure equalization must first be carried out between the suspension cylinder 10 and the suspension reservoirs 16, 18.

[0019] In order to achieve this pressure equalization, in a first step, as illustrated in FIG. 2, the 3/2-way valve 50 is activated and the other line 42 connected to the hydraulic pump P. Since the switching valve 48 remains in its unactuated position as illustrated, the pump pressure is blocked by the switching valve 48 in the other connecting line 54 in the direction of the first line 40. If the pressure on the piston side 12 corresponds to the load pressure required, movement begins immediately on the suspension cylinder 10 and the piston 22 with piston rod 24 begins to travel in the direction of the piston side 12 of the suspension cylinder 10. The pressure in the suspension reservoir 16 may be even lower than the pressure on the piston side 12 of the suspension cylinder 10. In particular, the excess amount of fluid in movement for the purpose as indicated by the arrow from the piston side 12 is expelled in the direction of the side branch.

[0020] If the pressure on the piston side 12 is above the required load pressure m, first fluid, especially hydraulic fluid, is drained from the suspension reservoir 16 by way of the 2/2-way switching valve 44 as indicated by the arrow in FIG. 3 to the tank T, until the load pressure m has been reached. Once the load pressure has been reached, movement of the suspension cylinder 10 begins and the cylinder travels in the direction of the arrow. When the suspension cylinder starts to travel, hydraulic fluid is drawn from the associated reservoir 18 on the ring or rod side 14 of the suspension cylinder 10 and so pressure equalization is established between cylinder pressure on the rod side 14 and reservoir pressure for the suspension reservoir 18 at system pressure. If the control system (sensor device, data interpretation unit) detects movement at the system suspension cylinder 10, the first step toward pressure equalization has been completed. The pressure on the rod side 14 of the suspension cylinder 10 then corresponds to the storage pressure of the associated suspension cylinder 18 and both pressure values correspond to the system pressure. The valve 46 is subsequently actuated and then assumes a switch position as shown in FIG. 4.

[0021] The next, second, step to pressure equalization now consists in switching of both the 3/2-way switching valve 50 and the 3/2 way switching valve 48 to the position allowing supply of line 40 or 42. In the switching state shown in FIG. 4 and achieved for this purpose, the piston 22 with piston rod 24 now emerges from the suspension cylinder 10 in the direction of the arrow. If the reservoir pressure of the suspension reservoir 16 now corresponds to the required load pressure m, movement at the suspension cylinder 10 begins immediately and the suspension cylinder 10 is extended. But if the reservoir pressure at the suspension reservoir 16 is initially lower than the required load pressure m, in a first step the suspension reservoir 16 is charged to load pressure by way of the associated return valve 34 in the line 40. If the load pressure has been reached, movement begins at the suspension cylinder 10 and the piston 22 with piston rod 24 is extended. Since the system of piston 22 and piston rod 24 rests on the unsprung mass which customarily may be in contact with the ground, extension of the system of piston 12 and piston rod 24 is equivalent to lifting of the sprung mass. In the case of the extension movement of the suspension cylinder 10 referred to, the pressure on the piston side 12 equals the pressure in the suspension reservoir 16 and this in turn equals the load pressure m. The control unit referred to above, consisting essentially of the sensor device not shown in detail and the data interpretation unit, detects the movement at the suspension cylinder 10 and the pressure equalization is then considered to be complete. Valves 48 and 50 in turn are shifted to their blocked position as shown in FIG. 1 and after engagement of the upper 2/2-way switching valve 44 as seen in the line of sight to FIG. 4, the spring suspension is open, that is, both the piston side 12 and the rod side 14 are connected to the suspension reservoirs 16 and 18 associated with them in a fluid conducting state for a spring suspension process.

[0022] Equalization of pressure between suspension cylinder 10 and the associated reservoirs 16, 18 is effected by the circuitry shown and the switching process described, with slight movement at the suspension cylinder in one direction or the direction opposite it, independently of possible change load m, so that uncontrolled movement is prevented when the suspension is engaged.

[0023] In an embodiment of the invention not shown, the sprung masses maybe replaced by unsprung masses, the circuitry of the suspension system being more or less retained, that is, the hydraulic components described remain connected as illustrated both to the piston and to the rod cavity of the suspension cylinder 10, the advantages referred to being retained as a result of the exchange made for the purpose. In another embodiment (not shown) it is also possible to detect the differential pressure present upstream and downstream from the switching valve 44 with conventional measurement devices. In the event that no differential pressure (permissible tolerance: minimum differential pressure) exists, the second step for pressure equalization as described in the foregoing may be dispensed with and accordingly the spring suspension may be released even more quickly.

[0024] Only the most important components of the spring suspension system claimed for the invention are shown in the illustrations and corresponding throttles and return valves for damping of the system and the path-measuring system itself for measurement of movement of the state of the system at suspension cylinder 10 have been omitted from the circuit diagram. On the free end of the load monitoring device LS there is mounted a conventional variable capacity pump which controls the amount of fluids so that the level of the pressure reported by the load monitoring device LS is maintained. A closed control cycle is thereby obtained as a function of the pressure and load situation. 

1. A suspension system, in particular for a working machine such as a tractor or the like, having a suspension cylinder (10) to which varying load pressures (m) may be applied, the piston side (12) and rod side (14) of which suspension cylinder (10) may be connected to a suspension reservoir (16, 18) which locks the suspension, an equalization device (28) having a switching valve (48) for controlling the piston side (12) of the suspension cylinder (10) inside the supply device (30), and a pressure supply (p) for maintaining the system pressure required in the suspension system, characterized in that the equalization device (28) has another switching valve (50) inside the supply device (30) for controlling the rod side (14) of the suspension cylinder (10) and in that a load monitoring device (LS) which controls the pressure supply (p) for obtaining the system pressure required is connected to a branch (38) of a line (40) to elements of the locking device (20) for the piston side (12) and the associated suspension reservoir (16) for the piston side (12) of the suspension cylinder (10).
 2. The spring suspension system as claimed in claim 1, wherein the suspension reservoirs (16, 18) and the locking device (20) are connected to a supply device (30) as part of the equalization device (28), which provides connection optionally to a pressure supply source (P) and/or to a tank connection (T) by means of a switching device (32).
 3. The spring suspension system as claimed in claim 2, wherein the suspension reservoirs (16, 18) may be separated from the supply device (30) each by way of a return valve (34, 36) which is held spring loaded in its closed position and which assumes its opened position in the direction of the pertinent suspension reservoir (16, 18).
 4. The spring suspension system as claimed in claim 3, wherein the return valve (34) is connected to the line (40) between suspension reservoir (16) and a point of connection of the line (40) to the branch (38).
 5. The spring suspension system as claimed in claim 4, wherein the suspension reservoir (16) is connected to the line (40) by the return valve (34).
 6. The spring suspension system as claimed in one of claims 1, wherein the locking device (20) has for both the piston side (12) and for the rod side (14) of the suspension cylinder (18) a switching valve (44, 46), in particular a 2/2-way switching valve which when in its unactuated base position blocks the fluid conducting path to the associated suspension reservoir (16) and frees such path in the opposite direction.
 7. The suspension system as claimed of in claims 1 to 6, wherein the switching valves (48, 50) are in the form of 3/2-way switching valves which in the base position, in which no actuation has been effected, are connected to the tank connection (T) and on their admission side are connected to each other so as to conduct fluid.
 8. The spring suspension system as claimed in claim 7, wherein an opening control line (41) for a releasable return valve (43) is connected to a line (45) between the return valve (36) and the 3/2-way valve (50).
 9. The spring suspension system as claimed in claim 7 or 8, wherein the suspension cylinder (10), in particular the position of the piston rod (24), is monitored by a sensor device which transmits to a data interpretation unit its signals, which activate the switching valves (44, 46, 48, 50) for a switching process. 